Method of laser separation of the epitaxial film or the epitaxial film layer from the growth substrate of the epitaxial semiconductor structure (variations)

ABSTRACT

The present invention proposes variations of the laser separation method allowing separating homoepitaxial films from the substrates made from the same crystalline material as the epitaxial film. This new method of laser separation is based on using the selective doping of the substrate and epitaxial film with fine donor and acceptor impurities. In selective doping, concentration of free carries in the epitaxial film and substrate may essentially differ and this can lead to strong difference between the light absorption factors in the infrared region near the residual beams region where free carriers and phonon-plasmon interaction of the optical phonons with free carriers make an essential contribution to infrared absorption of the optical phonons. With the appropriate selection of the doping levels and frequency of infrared laser radiation, it is possible to achieve that laser radiation is absorbed in general in the region of strong doping near the interface substrate-homoepitaxial film. When scanning the interface substrate-homoepitaxial film with the focused laser beam of sufficient power, thermal decomposition of the semiconductor crystal takes place with subsequent separation of the homoepitaxial film. The advantage of the proposed variations of the method for laser separation of epitaxial films in comparison with the known ones is in that it allows the separation of homoepitaxial films from the substrates, i.e., homoepitaxial films having the same width of the forbidden gap as the initial semiconductor substrate has. The proposed variations of the method can be used for separation of the epitaxial films.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 14/129,594, filed on Dec. 27, 2013; which claims benefit of the U.S.National Phase of International Patent Application No.PCT/RU2012/000588, filed on Jul. 13, 2012; which claims benefit ofRussian Patent Application No. 2011129184, filed on Jul. 13, 2011, thecontents of which are incorporated herein by reference in theirentireties.

TECHNICAL FIELD

Group of the inventions relates to the laser treatment of the solidmaterials, in particular, to the method of separation of thesemiconductors' surface layers with laser radiation, namely the laserseparation of the epitaxial film or of the epitaxial film layer from thegrowth substrate of the epitaxial semiconductor structure.

BACKGROUND ART

Laser separation of the epitaxial layers of the semiconductor crystalsfrom the growth substrates with their transfer on to the ungrowthsubstrates is widely used now in manufacturing of the light diodes (U.S.Pat. No. 7,241,667, U.S. Pat. No. 7,202,141) and laser diodes (U.S. Pat.No. 6,365,429) according to the flip-chip technology.

In the first time, laser separation of the gallium nitride layers fromthe transparent growth sapphire substrates was proposed in the workKelly et al Physica Status Solidi (a) vol. 159, pp. R3, R4, (1997). Inthis work the ultraviolet excimer laser with wave length λ=355 nmsatisfying the ratio 2πhc/E_(g1)<λ<2πhc/E_(g2) was used, for which thequantum energy is within the forbidden gap of the substrate E_(g1) madeof sapphire, but exceeds the width of the forbidden gap of the epitaxialfilm E_(g2), consisting of gallium nitride.

Later, the method of laser separation based on the difference betweenthe widths of the forbidden gaps of the growth substrate and epitaxialfilm was improved. In particular, to improve quality of the separatedepitaxial film and to suppress its cracking, it was proposed to useadditional sacrifial layer with the width of the forbidden gap less thanthe widths of the forbidden gaps of the growth substrate and epitaxialfilm, as well to use scanning of the heteroepitaxial interface betweenthe growth substrate and epitaxial film (U.S. Pat. No. 6,071,795, U.S.Pat. No. 6,365,429).

The general scheme of the laser separation methods based on thedifference between the widths of the forbidden gaps of the growthsubstrate and epitaxial film is shown in FIG. 1.

When exposing to ultraviolet from the side of the substrate fromheteroepitaxial semiconductor gallium nitride film 102 grown on thesubstrate 101 of sapphire having the width of the forbidden gap morethan the light quantum energy, ultraviolet laser radiation passesthrough sapphire and is absorbed in the thin layer of gallium nitridenearby the heteroepitaxial interface 105 gallium nitride—sapphire. Onexposure to ultraviolet laser radiation, gallium nitride in the area 104defined by crossing of the ultraviolet laser radiation 103 withheteroepitaxial interface 105 is heated up to the temperature T₁,exceeding the decomposition temperature T₀˜900° C., and decomposes intogaseous nitrogen and liquid gallium, and as a result epitaxial film ofgallium nitride separates from sapphire.

All before proposed methods of laser separation of epitaxial films fromthe growth substrates are based on the difference between the widths ofthe forbidden gaps of the epitaxial film E_(g2) and substrate E_(g1).These methods can be successfully used for separating the epitaxialfilms obtained using heteroepitaxy method, i.e., technology of growingthe epitaxial film onto the growth substrate made of the material whichdiffers from the epitaxial film material.

However, to obtain high quality epitaxial films without integratedmechanical stresses, it is often happened to be necessary to use ahomoepitaxy method, which provides growing of the epitaxial film on thegrowth substrate from the same material as the epitaxial film. In thiscase growth substrate and epitaxial film have an equal width of theforbidden gap, and the usual laser separation method disclosed abovebecomes unapplied.

The object of the present invention is an expansion of the methodapplication field, namely providing the possibility of separating theepitaxial films from the substrates made of the same crystal material asthe epitaxial film.

SUMMARY OF INVENTION

To solve this object, two variations of the method for laser separationof the epitaxial film or epitaxial film layer from the growth substrateof the epitaxial semiconductor structure were proposed.

In the first variation of the method in growing the epitaxial film orepitaxial film layer, selective doping with small donor or acceptorimpurities of some areas of the epitaxial structure is used, so that theresulting concentration of the small impurities in the selectively dopedareas substantially exceeds the background concentration in the undopedareas. Then, the focused laser beam is directed onto the epitaxialstructure consisting of the substrate and epitaxial film so that thebeam focus is placed in the selectively doped areas of the crystalstructure in which absorption of the laser radiation takes place. Laserbeam is moved with scanning the selectively doped areas of the epitaxialstructures with beam focus with partial thermal decomposition ofselectively doped areas and decreasing their mechanical strength. Afterlaser scanning the epitaxial structure is glued on the temporarysubstrate and the epitaxial film or the epitaxial film layer isseparated from the growth substrate or the growth substrate with a partof the epitaxial film by applying mechanical or thermomechanical stress.

The second variation of the method is characterized by the samefeatures, and differs from the first method in that the epitaxialstructure is glued on the temporary substrate before laser scanning,then laser scanning of the epitaxial structure glued on the temporarysubstrate is performed, and after laser scanning the epitaxial film orthe epitaxial film layer is separated from the growth substrate or thegrowth substrate with a part of the epitaxial film by applyingmechanical or thermomechanical stress.

Preferably, the epitaxial film or the epitaxial film layer is grown bythe homoepitaxy method.

Preferably, the selectively doped area is the substrate or the surfacelayer of the substrate.

Preferably, the selectively doped area is the epitaxial film or thelower layer of the epitaxial film.

Preferably, the material of the crystalline structure consisting of thesubstrate and epitaxial film, is the semiconductor from the elements ofthe forth group or the semiconductor compound from the elements of theforth group, or the semiconductor compound from the elements of thethird and fifth group, or the semiconductor compound from the elementsof the second and sixth group of the periodic system.

Preferably, the laser wave length for separating the homoepitaxial filmsfrom the growth substrate is in the following wave length range: forsilicon, germanium and gallium arsenide semiconductors in the range of 6μm≤λ≤48 μm, for gallium nitride in the range of 4 μm≤λ≤32 μm, forsilicon carbide 3 μm≤λ≤24 μm, for alumina nitride in the range of 2.5μm≤λ≤20 μm, and for diamond 2 μm≤λ≤16 μm.

Preferably, infrared gas pulse pumped silicon dioxide CO₂ or siliconoxide CO is used as a laser.

The proposed variations of the laser separation method allow separatingthe homoepitaxial films from the substrates made of the same crystallinematerial as the epitaxial film. This new laser separation method isbased on the usage of the selective doping of the substrate andepitaxial film with the fine donor or acceptor impurities. In theselective doping, concentrations of the free carriers in the epitaxialfilm and substrate may significantly differ, and this can lead to astrong difference between the light absorption factors in the infraredregion near the region of the residual beams, where free carriers andphonon-plasmon interaction of the optical phonons with free carriersmake an essential contribution to infrared absorption of the opticalphonons.

With the appropriate selection of the doping levels and frequency ofinfrared laser radiation it is possible to achieve that laser radiationis absorbed in general in the region of strong doping near the interfacesubstrate-homoepitaxial film. When scanning the interfacesubstrate-homoepitaxial film with the focused laser beam of sufficientpower, thermal decomposition of the semiconductor crystal takes placewith subsequent separation of the homoepitaxial film.

To realize the proposed method of laser separation, it is preferably touse laser radiation with wave length λ being within the infrared regionof relative transparence of the undoped semiconductor, namely near theedge of the residual beams region where a strong absorption of light atthe expense of one- or two-phonon processes is not possible, but arelatively weak absorption of light may present at the expense of three-or more phonon processes.

Preferably, wave length λ of the laser beam is within the range ofc/4v₀≤λ≤2c/v₀, where v₀ is a frequency of LO-optical phonon for asemiconductor material of the growth substrate, c is a light velocity.

The inequality given above follows that the preferable laser wave lengthfor separating the homoepitaxial films from the growth substrate iswithin the following wave length ranges: for silicon, germanium andgallium arsenide semiconductors in the range of 6 μm≤λ≤48 μm, forgallium nitride in the range of 4 μm≤λ≤32 μm, for silicon carbide 3μm≤λ≤24 μm, for alumina nitride in the range of 2.5 μm≤λ≤20 μm, and fordiamond 2 μm≤λ≤16 μm.

The technical result of the proposed invention consists in offering anew method of laser separation of the epitaxial films in comparison withthe known ones which allows to separate homoepitaxial films from thesubstrates, i.e., homoepitaxial films having the same width of theforbidden gap as the initial semiconductor substrate. Also, the proposedmethod allows using the high-effective and inexpensive infrared gassilicon dioxide CO₂ or silicon oxide CO lasers for separation of theepitaxial films.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by the drawings in which the priorart is shown FIG. 1, schemes illustrating the realization of the presentinvention FIGS. 2-5, and calculated spectral dependences of the lightabsorption factor in gallium nitride at various levels of doping withfine donor impurities FIG. 6.

FIG. 1 shows the scheme of the known prior art method of laserseparation of the heteroepitaxial film of semiconductor crystal from aforeign growth substrate using focused laser radiation with wave lengthλ for which a light quantum energy is within the forbidden gap of thesubstrate E_(g1), and exceeds the width of the forbidden gap of theepitaxial film E_(g2) material.

FIG. 2 shows a scheme illustrating the proposed method of laserseparation of the homoepitaxial film from the semiconductor substrateconsisting of the same semiconductor material as the homoepitaxial film.The scheme illustrates laser separation for the case of selective dopingthe substrate and homoepitaxial film with fine donor or acceptorimpurities when the doping level in the homoepitaxial film exceeds thedoping level in the semiconductor substrate.

FIG. 3 shows a scheme illustrating the proposed method of laserseparation of the homoepitaxial film from the semiconductor substrateconsisting of the same semiconductor material as the homoepitaxial film.The scheme illustrates laser separation for the case of selective dopingthe substrate and homoepitaxial film with fine donor or acceptorimpurities when the doping level in the semiconductor substrate exceedsthe doping level in the homoepitaxial film.

FIG. 4 shows a scheme illustrating the proposed method of laserseparation of the undoped upper layer of the homoepitaxial film from theundoped semiconductor substrate with a laser beam passing through thesubstrate and absorbed in the lower level of the homoepitaxial filmdoped with fine donor or acceptor impurities.

FIG. 5 shows a scheme illustrating the proposed method of laserseparation of the undoped upper layer of the homoepitaxial film from theundoped semiconductor substrate with a laser beam passing through theupper undoped layer and absorbed in the lower level of the homoepitaxialfilm doped with fine donor or acceptor impurities.

FIG. 6 shows the calculated spectral dependences of the light absorptionfactor near the residual beams region for semiconductor crystal ofgallium nitride at various levels of doping with fine donor impurities.Dependences 601, 602 and 603 refer to the doping levels 10¹⁷, 10¹⁸ and5·10¹⁹ cm⁻³ respectively.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will become readily apparent from the followingdetailed description of exemplary embodiments. It should be noted thatthe consequent description of these embodiments is only illustrative,but not exhaustive.

Example 1

Separation of homoepitaxial gallium nitride film doped with fine donorimpurities from the undoped semiconductor gallium nitride substrate withlaser beam passing through the substrate.

FIG. 2 shows a scheme of laser separation of homoepitaxial galliumnitride film 202, 50 μm wide from the semiconductor gallium nitridesubstrate 101, 200 μm wide. Level of doping with fine silicon donorimpurities in the homoepitaxial film 202 is of 5·10¹⁹ cm⁻³, and exceedsthe background concentration of fine oxygen and silicon donors in thesemiconductor substrate 101 equalled 10¹⁷ cm⁻³.

For separating of the homoepitaxial gallium nitride film, CO₂ pulsepumped laser is used operating at the wave length λ=10.6 μm andgenerating pulses of energy 0.1 J, duration 50 ns and repetition rate100 Hz.

Absorption factor of laser radiation with wave length λ=10 μm in thehomoepitaxial gallium nitride film 202 doped with fine silicon donorimpurities of concentration 5·10¹⁹ cm⁻³, equals 4·10⁴ cm⁻¹, whereas theabsorption factor of this radiation in the undoped semiconductor galliumnitride substrate 101 with background concentration of fine oxygen andsilicon donors equalled 10¹⁷ cm⁻³ is 5·10¹ cm⁻¹.

The respective spectral dependences of the light absorption factor nearthe residual beams region which we calculated for the semiconductorgallium nitride crystals with different levels of doping with fine donorimpurities are given in FIG. 6. The curves 601, 602 and 603 refer to thedoping levels 10¹⁷, 10¹⁸ and 5·10¹⁹ cm³ respectively.

Scheme in FIG. 2 shows that infrared laser beam 203 passes through thesubstrate 101 and is focused into the spot 1 mm in diameter whichprovides the energy density of 10 J/cm². Under the action of infraredlaser beam 203 of pulse CO₂ laser with wave length λ=10 μm focused intothe spot 1 mm in diameter weakly absorbed in the undoped semiconductorgallium nitride substrate 101 and strongly absorbed in the homoepitaxialgallium nitride film 202 doped with fine donor impurities, local heatingof the homoepitaxial film 202 takes place in the region 204 defined bycrossing of the infrared laser beam 203 with the homoepitaxial interface205 between the undoped semiconductor substrate 101 and the dopedhomoepitaxial film 202. Local heating above temperature 900° C. leads tochemical decomposition of gallium nitride crystal into gaseous nitrogenand liquid gallium in the region 204. Movement of the laser beam 203focus with velocity of 10 cm/s in the horizontal plane which is parallelto homoepitaxial interface 205 leads to subsequent decomposition ofgallium nitride in the set of regions 204 and weakening of thehomoepitaxial interface 205 between the undoped semiconductor substrate101 and the doped homoepitaxial film 202. Then when pasting thehomoepitaxial film 202 on the temporary metallic ceramic or plasticsubstrate and applying small mechanical or thermomechanical stress it ispossible to separate the homoepitaxial film 202 from the substrate 101.

Example 2

Separation of undoped homoepitaxial gallium nitride film fromsemiconductor gallium nitride substrate doped with fine donorimpurities, by means of laser beam passing through the homoepitaxialfilm.

FIG. 3 shows the scheme of laser separation of undoped homoepitaxialgallium nitride film 100 μm thick from semiconductor gallium nitridesubstrate 1 mm thick. The background concentration of fine oxygen andsilicon donors in the homoepitaxial film 202 is 10¹⁷ cm⁻³ and isessentially less than the concentration of fine silicon donor impuritiesin the doped semiconductor substrate 101 equalled 5·10¹⁹ cm⁻³.

For separating of the homoepitaxial gallium nitride film, CO₂ pulsepumped laser is used operating at the wave length λ=10.6 μm andgenerating pulses of energy 0.1 J, duration 50 ns and repetition rate100 Hz. Absorption factor of laser radiation with wave length λ=10 μm inthe undoped homoepitaxial gallium nitride film 202, with backgroundconcentration of fine oxygen and silicon donors equalled 10¹⁷ cm⁻³, isof 5·10¹ cm⁻¹, whereas the absorption factor of this radiation in thesemiconductor gallium nitride substrate 101 doped with fine silicondonor impurities of concentration 5·10¹⁹ cm⁻³, equals 4·10⁴ cm⁻¹. Therespective spectral dependences of the light absorption factor near theresidual beams region which we calculated for the semiconductor galliumnitride crystals with different levels of doping with fine donorimpurities are given in FIG. 6. The curves 601, 602 and 603 refer to thedoping levels 10¹⁷, 1018 and 5·10¹⁹ cm³ respectively.

Scheme in FIG. 3 shows that the infrared laser beam 203 passes throughhomoepitaxial film 202 and focused into the spot 1 mm in diameter whichprovides the energy density of 10 J/cm².

Under the action of infrared laser beam 203 of pulse CO₂ laser with wavelength λ=10.6 μm focused into the spot 1 mm in diameter weakly absorbedin the undoped homoepitaxial gallium nitride film 202 and stronglyabsorbed in the semiconductor gallium nitride substrate 101 doped withfine donor impurities, local heating of the substrate 101 takes place inthe region 204 defined by crossing of the infrared laser beam 203 withthe homoepitaxial interface 205 between the doped semiconductorsubstrate 101 and the undoped homoepitaxial film 202. Local heatingabove temperature 900° C. leads to chemical decomposition of galliumnitride crystal into gaseous nitrogen and liquid gallium in the region204. Movement of the laser beam 203 focus with velocity of 10 cm/s inthe horizontal plane which is parallel to homoepitaxial interface 205leads to the subsequent decomposition of gallium nitride in the set ofregions 204 and to weakening of the homoepitaxial interface 205 betweenthe doped semiconductor substrate 101 and the undoped homoepitaxial film202. Then when pasting the homoepitaxial film 202 on the temporarymetallic, ceramic or plastic substrate and applying a small mechanicalor thermomechanical stress it is possible to separate the homoepitaxialfilm 202 from the substrate 101.

Example 3

Separation of the undoped upper layer of the homoepitaxial galliumnitride film from the undoped semiconductor gallium nitride substratewith laser beam passing through the substrate and absorbed in lowerlayer of homoepitaxial film doped with fine donor impurities. FIG. 4shows the scheme of laser separation of the undoped homoepitaxialgallium nitride film 202, 50 μm thick from the undoped semiconductorgallium nitride substrate 101, 200 μm thick using the doped lower layer406 of the homoepitaxial film, 1 μm thick. Level of doping with finesilicon donor impurities in the lower layer 406 of the homoepitaxialgallium nitride film is 5·10¹⁹ cm⁻³ and exceeds the backgroundconcentration of fine silicon and oxygen donor impurities in thesemiconductor substrate 101 and the upper layer of the homoepitaxialfilm 202 equaled 10¹⁷ cm³.

For separating of the homoepitaxial gallium nitride film, CO₂ pulsepumped laser is used operating at the wave length λ=10.6 μm andgenerating pulses of energy 0.1 J, duration 50 ns and repetition rate100 Hz.

Absorption factor of laser radiation with wave length λ=10.6 μm in thelower layer 406 of the homoepitaxial gallium nitride film doped withfine silicon donor impurities with concentration 5·10¹⁹ cm⁻³ equals4·10⁴ cm⁻¹, whereas the absorption factor of this laser radiation in theundoped semiconductor gallium nitride substrate 101 and in the undopedupper layer 402 of the homoepitaxial gallium nitride film withbackground concentrations of fine oxygen and silicon donors of 10¹⁷ cm⁻³equals 5·10¹ cm⁻¹.

The respective spectral dependences of the light absorption factor nearthe residual beams region which we calculated for the semiconductorgallium nitride crystals with different levels of doping with fine donorimpurities are given in FIG. 6. The curves 601, 602 and 603 refer to thedoping levels 10¹⁷, 10¹⁸ and 5·10¹⁹ cm³ respectively.

Scheme in FIG. 4 shows that the laser beam 203 passes through thesubstrate 101 and is focused into the spot 1 mm in diameter whichprovides the energy density of 10 J/cm². Under the action of infraredlaser beam 203 of pulse CO₂ laser with wave length λ=10.6 μm focusedinto the spot 1 mm in diameter weakly absorbed in the undopedsemiconductor gallium nitride substrate 101 and strongly absorbed in thelower layer 406 of the homoepitaxial gallium nitride film 202 doped withfine donor impurities, local heating of the lower layer 406 of thehomoepitaxial film takes place in the region 404, defined by crossing ofthe infrared laser beam 203 with the homoepitaxial interface 405 betweenthe undoped semiconductor substrate 101 and the doped lower layer 406 ofthe homoepitaxial film 202. Local heating above temperature 900° C.leads to chemical decomposition of gallium nitride crystal into gaseousnitrogen and liquid gallium in the region 404. Movement of the laserbeam 203 focus with velocity of 10 cm/s in the horizontal plane which isparallel to homoepitaxial interface 405 leads to the subsequentdecomposition of gallium nitride in the set of regions 404 and toweakening of the homoepitaxial interface 405 between the undopedsemiconductor substrate 101 and the doped lower layer 406 of thehomoepitaxial film. Then when pasting the undoped upper layer 402 of thehomoepitaxial film on the temporary metallic, ceramic or plasticsubstrate and applying a small mechanical or thermomechanical stress itis possible to separate the undoped upper layer 402 of the homoepitaxialfilm with non-evaporated part of the lower doped layer 406 from thesubstrate 101.

Example 4

Separation of the undoped upper layer of the homoepitaxial galliumnitride film from the undoped semiconductor gallium nitride substratewith laser beam passing through the upper layer of the homoepitaxialfilm and absorbed in lower layer of homoepitaxial film doped with finedonor impurities.

FIG. 5 shows a scheme of laser separation of the undoped layer of thehomoepitaxial gallium nitride film 202, 100 μm thick from the undopedsemiconductor gallium nitride substrate 101, 2 μm thick using the dopedlower layer 406 of the homoepitaxial gallium nitride film 1 μm thick.Level of doping with fine silicon donor impurities in the lower layer406 of the homoepitaxial gallium nitride film is 5·10¹⁹ cm³, and exceedsbackground concentration of fine oxygen and silicon donor in thesemiconductor substrate 101 and in the upper layer 402 of thehomoepitaxial film equaled 10¹⁷ cm³.

For separating of the homoepitaxial gallium nitride film, CO₂ pulsepumped laser is used operating at the wave length λ=10.6 μm andgenerating pulses of energy 0.1 J, duration 50 ns and repetition rate100 Hz.

Absorption factor of laser radiation with wave length λ=10.6 μm in thelower layer 406 of the homoepitaxial gallium nitride film doped withfine silicon donor impurities with concentration 5·10¹⁹ cm⁻³ equals4·10⁴ cm⁻¹, whereas the absorption factor of this laser radiation in theundoped semiconductor gallium nitride substrate 101 and in the undopedupper layer 402 of the homoepitaxial gallium nitride film withbackground concentrations of fine oxygen and silicon donors of 10¹⁷ cm⁻³equals 5·10¹ cm⁻¹.

The respective spectral dependences of the light absorption factor nearthe residual beams region which we calculated for the semiconductorgallium nitride crystals with different levels of doping with fine donorimpurities are given in FIG. 6. The curves 601, 602 and 603 refer to thedoping levels 10¹⁷, 10¹⁸ and 5·10¹⁹ cm³ respectively.

Scheme in FIG. 5 shows that the laser beam 203 passes through the upperlayer 402 of the homoepitaxial film and is focused into the spot 1 mm indiameter which provides the energy density of 10 J/cm². Under the actionof infrared laser beam 203 of pulse CO₂ laser with wave length λ=10.6 μmfocused into the spot 1 mm in diameter weakly absorbed in the undopedupper layer 402 of the homoepitaxial gallium nitride film and stronglyabsorbed in the lower layer 406 of the homoepitaxial gallium nitridefilm doped with fine donor impurities, local heating of the lower layer406 of the homoepitaxial gallium nitride film takes place in the region404 defined by crossing of the infrared laser beam 203 with theinterface 505 between the undoped upper layer 402 and the doped lowerlayer 406 of the homoepitaxial gallium nitride film. Local heating abovetemperature 900° C. leads to chemical decomposition of gallium nitridecrystal into gaseous nitrogen and liquid gallium in the region 404.Movement of the laser beam 203 focus with velocity of 10 cm/s in thehorizontal plane which is parallel to the interface 405 leads to thesubsequent decomposition of gallium nitride in the set of regions 404and to weakening of the interface 405 between the undoped upper layer402 and the doped lower layer 406 of the homoepitaxial film. Then whenpasting the undoped upper layer 402 of the homoepitaxial film on thetemporary metallic, ceramic or plastic substrate and applying a smallmechanical or thermomechanical stress it is possible to separate theundoped upper layer 402 of the homoepitaxial film from thenon-evaporated part of the lower doped layer 406 and from the substrate101.

Example 5

Separation of the undoped homoepitaxial silicon carbide 4H-SiC film fromthe semiconductor silicon carbide 4H-SiC substrate doped with fine donorimpurities by means of the laser beam passing through the homoepitaxialfilm.

FIG. 3 shows a scheme of laser separation of the undoped homoepitaxialsilicon carbide 4H-SiC film 202, 100 μm thick from the semiconductorsilicon carbide 4H-SiC substrate 101, 400 μm thick. The backgroundconcentration of the fine donors in the epitaxial film 202 is less than10¹⁷ cm⁻³, and essentially less than the concentration of the finenitrogen donor impurities in the doped semiconductor substrate 101equaled 5·10¹⁹ cm⁻³.

For separating of the homoepitaxial silicon carbide 4H-SiC film, COpulse pumped laser is used operating at the wave length λ=5.2 μm andgenerating pulses of energy 0.4 J, duration 50 ns and repetition rate 10Hz. Absorption factor of laser radiation with wave length λ=5.2 μm inthe undoped homoepitaxial silicon carbide 4H-SiC film 202, with thebackground concentration of the fine donors less than 10¹⁷ cm⁻³ is 10cm⁻¹ (A. M. Hofmeister, K. M. Pitman, A. F. Goncharov, and A. K. SpeckThe Astrophysical Journal, 696:1502-1516, 2009 May 10), whereas theabsorption factor of this radiation in the semiconductor silicon carbide4H-SiC substrate 101 doped with the fine nitrogen donor impurities ofconcentration 5·10¹⁹ cm⁻³ exceeds 10⁴ cm⁻¹.

Scheme in FIG. 3 shows that the infrared laser beam 203 passes throughthe homoepitaxial film 202 and is focused into the spot 1 mm in diameterwhich provides the energy density of 50 J/cm².

Under the action of infrared laser beam 203 of pulse CO laser with wavelength λ=5.2 μm focused into the spot 1 mm in diameter weakly absorbedin the undoped homoepitaxial silicon carbide 4H-SiC film 202 andstrongly absorbed in the semiconductor silicon carbide 4H-SiC substrate101 doped with the fine donor impurities, local heating of the substrate101 takes place in the region 204, defined by crossing of the infraredlaser beam 203 with the interface 205 between the doped semiconductorsubstrate 101 and undoped homoepitaxial film 202. Local heating totemperature above 2800° C. leads to chemical decomposition of siliconcarbide 4H-SiC of the gallium nitride crystal into silicon and carbon inthe region 204. Movement of the laser beam 203 focus with velocity of 2cm/s in the horizontal plane which is parallel to the interface 205leads to subsequent decomposition of silicon carbide 4H-SiC in the setof regions 204 and to weakening of the interface 205 between the dopedsemiconductor substrate 101 and the undoped homoepitaxial film 202. Thenwhen pasting the epitaxial film 202 on the temporary metallic, ceramicor plastic substrate and applying a small mechanical or thermomechanicalstress it is possible to separate the epitaxial film 202 from thesubstrate 101.

Example 6

Separation of weakly doped homoepitaxial silicon film from thesemiconductor silicon substrate strongly doped with fine boron acceptorimpurities using laser beam passing through the homoepitaxial film.

FIG. 3 shows the scheme of laser separation of weakly dopedhomoepitaxial silicon film 202, 50 μm thick from the semiconductorsilicon substrate 101, 700 μm thick. Concentration of the fine boronacceptor impurities equals 10¹⁷ cm³, and essentially less than theconcentration of the fine boron acceptor impurities in the dopedsemiconductor substrate 101 equaled 10¹⁹ cm⁻³.

For separating of the homoepitaxial silicon film, CO₂ pulse pumped laseris used operating at the wave length λ=10.6 μm and generating pulses ofenergy 0.1 J, duration 50 ns and repetition rate 100 Hz.

Absorption factor of laser radiation with the wave length λ=10.6 μm inthe weakly doped homoepitaxial silicon film 202 with concentration offine acceptors of 10¹⁷ cm³ is 12 cm⁻¹ (Hara, H. and Y. Nishi, J. Phys.Soc. Jpn 21, 6, 1222, 1966), whereas the absorption factor of thisradiation in the semiconductor silicon substrate 101 doped with the fineboron acceptor impurities of concentration 10¹⁹ cm³ equals 3000 cm⁻¹.

Scheme in FIG. 3 shows that the infrared laser beam 203 passes throughthe homoepitaxial film 202 and is focused into the spot 0.5 mm indiameter which provides the energy density of 40 J/cm².

Under the action of infrared laser beam 203 of pulse CO₂ laser with wavelength λ=10.6 μm focused into the spot 0.5 mm in diameter weaklyabsorbed in the undoped homoepitaxial silicon film 202 and stronglyabsorbed in the semiconductor silicon substrate 101 doped with fineboron acceptor impurities, local heating of the substrate 101 takesplace in the region 204, defined by crossing of the infrared laser beam203 with the interface 205 between the strongly doped semiconductorsubstrate 101 and weakly doped homoepitaxial film 202. Local heating totemperature above 1400° C. leads to partial melting and amorphicity ofthe silicon crystal in the region 204. Movement of the laser beam 203focus with velocity of 20 cm/s in the horizontal plane which is parallelto the interface 205 leads to subsequent melting and amorphycity ofsilicon crystal in the set of regions 204 and to weakening of theinterface 205 between the strongly doped semiconductor substrate 101 andweakly doped homoepitaxial film 202. Then when pasting the epitaxialfilm 202 on the temporary metallic, ceramic or plastic substrate andapplying a small mechanical or thermomechanical stress it is possible toseparate the epitaxial film 202 from the substrate 101.

Despite the fact that the present invention was described andillustrated by the examples of the invention embodiments it should benoted that the present invention is in no case limited by the examplesgiven.

The invention claimed is:
 1. A method of laser separation of anepitaxial film or of an epitaxial film layer from a growth substrate ofan epitaxial semiconductor structure, the method comprising: usingselective doping of some regions of the epitaxial semiconductorstructure with fine donor or acceptor impurities when growing theepitaxial film or the epitaxial film layer, so that a resultingconcentration of fine donor or acceptor impurities in selectively dopedregions essentially exceeds a background concentration in undopedregions; gluing the epitaxial semiconductor structure onto a temporarysubstrate; directing a focused laser beam of a laser to the epitaxialsemiconductor structure glued onto the temporary substrate so as toplace a beam focus of the focused laser beam in the selectively dopedregions of the epitaxial semiconductor structure in which absorption oflaser radiation takes place; moving the focused laser beam so as to scanthe selectively doped regions of the epitaxial semiconductor structurewith the beam focus with partial thermal decomposition of theselectively doped regions and weakening of their mechanical strength;and separating the epitaxial film or the epitaxial film layer from thegrowth substrate or from the growth substrate with a part of theepitaxial film by applying mechanical or thermomechanical stress.
 2. Themethod according to claim 1, wherein the epitaxial film or the epitaxialfilm layer is grown by a homoepitaxy method.
 3. The method according toclaim 1, wherein a selectively doped region is a substrate or a surfacelayer of the substrate.
 4. The method according to claim 1, wherein aselectively doped region is the epitaxial film or a lower layer of theepitaxial film.
 5. The method according to claim 1, wherein a materialof the epitaxial semiconductor structure is a semiconductor from anelement of fourth group of the periodic system.
 6. The method accordingto claim 1, wherein a material of the epitaxial semiconductor structureis a semiconductor compound from elements of fourth group of theperiodic system.
 7. The method according to claim 1, wherein a materialof the epitaxial semiconductor structure is a semiconductor compoundfrom elements of third and fifth groups of the periodic system.
 8. Themethod according to claim 1, wherein a material of the epitaxialsemiconductor structure is a semiconductor compound from elements ofsecond and sixth group of the periodic system.
 9. The method accordingto claim 1, wherein for separating the epitaxial film or the epitaxialfilm layer from the growth substrate, the method comprises using thelaser with a wave length which is within following wave length ranges:for silicon, germanium and gallium arsenide semiconductors within a wavelength range of 6 μm≤λ≤48 μm; for gallium nitride within a wave lengthrange of 4 μm≤λ≤32 μm; for silicon carbide within a wave length range of3 μm≤λ≤24 μm; for alumina nitride within a wave length range of 2.5μm≤λ≤20 μm; and for diamond within a wave length range of 2 μm≤λ≤16 μm.10. The method according to claim 1, wherein the laser is an infraredgas pulse pumped CO₂ or CO laser.